1. Field of the Invention
The present invention relates to an upward-flow manganese contact column used for treating manganese-containing water.
2. Description of the Related Art
In a water treatment plant using underground water and ground surface water as water sources, tap water is sometimes darkened when raw water contains manganese ions. Accordingly, manganese sand has been used for removing manganese ions. In this method, manganese sand prepared by coating the surface of sand grains with manganese dioxide is packed in a tank, raw water is allowed to flow as upward-flow or downward-flow through a gravel layer under the sand layer with injection of chlorine, and manganese ions are removed from raw water by allowing manganese ions to precipitate as insoluble manganese by taking advantage of catalytic action of manganese dioxide.
However, it has been a problem in the related art that removal efficiency of manganese from raw water is low since manganese sand having a specific surface area of about 2 m2/g has been used. In addition, since the specific gravity of manganese sand is as low as 2.5 or less, the flow speed of raw water supplied to the manganese sand layer cannot be increased in order to prevent the sand from being washed away by the upward-flow. Consequently, the volume of the equipment per unit volume of treatment water becomes large.
The applicant of the present invention has developed a method for removing manganese ions using a manganese catalyst composed of β-manganese dioxide with a specific surface area of about 1.5 m2/g and a ceramic separation membrane, and acquired patent rights as Japanese Patent Nos. 3,705,590 and 3,786,885. The flow speed of upward-flow is increased as compared with related arts while the volume of equipment per unit volume of treatment water is decreased in this method for removing manganese ions, because the specific surface area of the manganese catalyst is large while the specific gravity thereof is as large as about 3.5.
However, when a layer packed with the manganese catalysts is formed on the gravel layer as in the related art, the manganese catalysts are sank into spaces between gravels due to large specific gravity of the manganese catalysts. As a result, manganese ions in raw water adhere to and grow on the surface of the gravels, which tend to be thickened. Therefore, the gravel layer is blocked to make it difficult to continuously operate the water treatment plant. This method (gravel supported method) is shown in FIG. 7.
Since the specific gravity of the manganese catalyst is large, there is a tendency that portions where raw water is readily spouted and portions where raw water is hardly spouted are formed due to a slight difference of pressure loss at the raw water spouting portions, and biased current is formed. Furthermore, particles of the manganese catalyst collide against one another at high speed when the flow rate of raw water at the raw water spouting portions is increased. Consequently, the surface of the catalyst is worn to reduce the amount of the manganese catalyst with a decrease of treatment ability, or the concentration of manganese ions increases in the effluent.